Time of arrival information passing in a distributed antenna system

ABSTRACT

Embodiments described herein provide for a method for obtaining location information regarding a wireless unit in a distributed antenna system (DAS). The method includes identifying a first time of arrival of a wireless signal in a time and frequency unit at a first active antenna unit (AAU). A second time of arrival of the wireless signal in the time and frequency unit at a second AAU is also identified. A location of a wireless unit transmitting the wireless signal is estimated based on a location of the first AAU, a location of the second AAU, and a difference between the first time of arrival and the second time of arrival. The location of the wireless unit and an indication that the location corresponds to the time and frequency unit is sent to a baseband unit or serving mobile location center (SMLC).

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation application of U.S. patent application Ser. No.14/918,182 filed Oct. 20, 2015 and titled “Time of Arrival InformationPassing in a Distributed Antenna System,” which claims the benefit ofU.S. Provisional Patent Application Ser. No. 62/066,076, filed on Oct.20, 2014, all of which are hereby incorporated herein by reference.

BACKGROUND

A conventional distributed antenna system (DAS) provides indoor oroutdoor coverage for wireless communications. Transmitted signals aredivided among several antennas in distributed locations to provideenhanced coverage as opposed to a single location transmitter. It can bedesired to locate a wireless device with a DAS, for example, foremergency purposes (e.g., 911 calls). However, because the receivedsignals from the distributed antennas are typically combined in theuplink before reaching a corresponding baseband unit or a serving mobilelocation center (SMLC), the baseband unit or SMLC may not be able toaccurately determine the location of the wireless device on its own.

SUMMARY

Embodiments described herein provide for a method for obtaining locationinformation regarding a wireless unit in a distributed antenna system(DAS). The method includes identifying a first time of arrival of awireless signal in a time and frequency unit at a first active antennaunit (AAU). A second time of arrival of the wireless signal in the timeand frequency unit at a second AAU is also identified. A location of awireless unit transmitting the wireless signal is estimated based on alocation of the first AAU, a location of the second AAU, and adifference between the first time of arrival and the second time ofarrival. The location of the wireless unit and an indication that thelocation corresponds to the time and frequency unit is sent to abaseband unit or serving mobile location center (SMLC).

DRAWINGS

Understanding that the drawings depict only examples and are nottherefore to be considered limiting in scope, the examples will bedescribed with additional specificity and detail through the use of theaccompanying drawings.

FIG. 1 is a block diagram of an example distributed antenna system.

FIG. 2 is a flow diagram of an example method for estimating a locationof a wireless unit using the DAS of FIG. 1.

In accordance with common practice, the various described features arenot drawn to scale but are drawn to emphasize specific features relevantto the examples. Like reference numbers and designations in the variousdrawings indicate like elements.

DETAILED DESCRIPTION

Embodiments described below relate to a method for estimating a locationof a wireless device using a distributed antenna system (DAS). In anexample, a time of arrival of a wireless signal at different antennas inthe DAS is identified and the DAS estimates a location of a wirelessunit based on these times of arrival. The DAS, however, does not knowthe identity of the wireless unit; therefore the DAS sends to a basebandunit, the location and an indication of an uplink time and frequencyunit that the wireless signal occupied.

FIG. 1 is a block diagram of an example communication system including aDAS 100. DAS 100 is communicatively coupled to a base station 115. DAS103 is used to transport communication signals between one or moreupstream devices (for example, base station 115, wireless access points,or other sources of radio frequency signals) and one or more downstreamwireless devices (for example, wireless units 128). In some embodiments,base station 115 is a part of a telecommunication-service providers'infrastructure and wireless units 128 comprise customer premiseequipment. Base station 115 is an RF source that performs basebandprocessing such as a baseband unit, a cellular base station (e.g.,eNodeB), or base transceiver station (BTS), for example. For simplicity,a single base station 115 is often referred to herein, however, itshould be understood that, in some embodiments, the interactionsdescribed herein can be performed with multiple base stations 115. TheRF source can be a standalone unit or can be implemented as part of acentralized/cloud RAN configuration where multiple baseband units areimplemented at a centralized location.

DAS 103 comprises a host unit 105 communicatively coupled to one or moreactive antenna units 110-1 to 110-n. In this embodiment, DAS 103 alsoincludes an intervening device 111 (which may comprise an intermediateor expansion unit, for example) communicatively coupled between hostunit 105 and one or more AAUs (AAU 110-2 shown in FIG. 1) to expand therange of host unit 105. Each active antenna unit 110-1 to 110-n includesone or more antennas which are used to communicate wirelessly withwireless units 128. Although in this embodiment a certain number ofactive antenna units 110-1 to 110-n and intervening units 111 arecoupled to host unit 105, in other embodiments other numbers of activeantenna units 110-1 to 110-n and intervening units 111 are coupled tohost unit 105. Also, other DAS topologies can be used. For example, oneor more host units can be daisy chained together. Also, one or more AAUscan be daisy chained together. Also, the daisy chains can form rings aswell as non-ring topologies.

As shown in FIG. 1, host unit 105 is coupled to AAUs 110-1 to 110-n andintervening unit 111 through bi-directional point-to-point communicationlinks 125. In an embodiment, communication links 125 comprise fiberoptic cables. In other embodiments, however, other communications meanssuch as but not limited to co-axial cables, twisted pair cables (e.g.,CAT-5, CAT-6 cables), or microwave communication links may be utilizedin various combinations.

Host unit 105 is communicatively coupled to one or more upstream devices(such as one or more base stations 115 or wireless access points). Insome embodiments, host unit 105 is coupled to the one or more upstreamdevices via a physical communication medium. In other embodiments, hostunit 105 is communicatively coupled to the one or more upstream devicesin other ways (for example, using one or more donor antennas and one ormore bi-directional amplifiers or repeaters). In an embodiment, basestation 115 comprises an eNodeB.

DAS 103 distributes communication signals between wireless units 128 andbase station 115. Wireless units 128 transmit/receive signals to/fromactive antenna units 110-1 to 110-n.

In the downlink direction, DAS 103 operates as a point-to-multipointtransport for signals from one or more base stations 115 to one or morewireless units 128. Downlink base station signals are received by DAS103 at host unit 105 from the base station 115. The DAS 103 generatestransport signals based on the downlink base station signals and sendsthe transport signals to each of the AAUs 110-1 to 110-n. In an example,each of the AAUs 110-1 to 110-n in DAS 103 receive identical transportsignals. In other examples, one or more subsets of the AAUs 110-1 to110-n receive different transport signals. Each AAU 110-1 to 110-Nconverts the transport signal from the host unit 105 into an analog RFwaveform and transmits the RF waveform to one or more of the wirelessunits 128 as an over-the-air modulated RF signal. Each AAU 110-1 to110-N includes a digital-to-analog converter (DAC) (in digitalimplementations) and radiohead hardware to perform the operations forproducing the analog modulated RF waveform from the received transportsignal and amplifying the analog modulated RF waveform for broadcast asan over-the-air RF signal.

In the uplink direction, each of the AAUs 110-1 to 110-n senses one ormore RF signals from one or more wireless units 128 and generates arespective uplink transport signal based on the one or more RF signals.The AAUs 110-1 to 110-n send their respective transport signals to thehost unit 105, and the host unit 105 aggregates the information from thetransport signals to provide a unified base station signal to the basestation 115.

The base station signals communicated between the base station 115 andDAS 103 (i.e., between the base station 115 and host unit 105) can bemodulated analog signals or signals including digital samplescorresponding to a modulated analog signal. The analog signals can beintermediate frequency (IF) or radio frequency (RF) signals. The digitalsamples can include samples corresponding to a baseband, intermediatefrequency (IF), or radio frequency (RF) version of the RF signals. Thebaseband samples can be complex I/Q samples and the IF and RF samplescan be real samples. The signals including digital samples correspondingto an analog modulated signal can conform to a base stationcommunication protocol such as the Common Public Radio Interface (CPRI),Open Base Station Architecture Initiative (OBSAI), or Open RadioEquipment Interface (ORI).

In a digital DAS example, the transport signals sent between the hostunit 105 and the AAUs 110-1 to 110-n include digital samplescorresponding to the modulated analog wireless signals sent and receivedbetween the AAUs 110-1 to 110-n and the wireless units 128. In thedownlink of such an example, the transport signal is a serial datastream including the digital samples. The digital samples can includesamples corresponding to a baseband, intermediate frequency (IF), orradio frequency (RF) version of the modulated analog signals. Thebaseband samples can be complex I/Q samples and the IF and RF samplescan be real samples.

In a first implementation of a digital DAS example, the signalscommunicated between the host unit 105 and the base station 115 aremodulated analog RF signals. In the downlink of this firstimplementation, the host unit 105 receives a modulated RF signal fromthe base station 115, down converts the RF signal to IF, digitizes (A/Dconverts) the IF signal to produce real digital IF samples, digitallydown-converts the real digital IF samples to produce I/Q (complex)samples, and incorporates the I/Q samples into a downlink transportsignal. In some embodiments, the I/Q samples are resampled. In someembodiments, any of the analog signals or digital samples can befiltered to select only a portion of the original bandwidth fortransport. In the uplink of this first implementation, the host unit 105receives an uplink transport signal from one more AAUs 110-1 to 110-n,extracts the I/Q samples therefrom, digitally up-converts the I/Qsamples to produce real digital IF samples, D/A converts the realdigital IF samples to a modulated analog IF signal, up-converts theanalog IF signal to an RF signal and sends the RF signal to the basestation 115. In some embodiments, digital samples from respectivetransport signals can be digitally summed to form unified data for thebase station 115.

In a second implementation of the digital DAS example, the signalscommunicated between the host unit 105 and the base station 115 carrydigital I/Q samples corresponding to a modulated analog signal. In thedownlink of this second implementation, the host unit 105 receives asignal from the base station 115 including digital I/Q samples (e.g., aCPRI signal) and incorporates the digital I/Q samples into a downlinktransport signal to the AAUs 110-1 to 110-n. In some embodiments, theI/Q samples are resampled. In some embodiments, the digital samples canbe filtered to select only a portion of the original bandwidth fortransport. In the uplink of this second implementation, the host unit105 receives an uplink transport signal from one or more AAUs 110-1 to110-n, extracts I/Q samples therefrom, and sends the I/Q samples to thebase station 115 (e.g., in a CPRI signal). In some embodiments, digitalsamples from respective transport signals can be digitally summed toform unified data for the base station 115.

In any case, in a digital DAS example, the transport signals carrypackets of digital samples corresponding to a modulated electromagneticradio-frequency waveform.

In an analog DAS example, the transport signals between the host unit105 and the AAUs 110-1 to 110-n include a modulated analog IF signal. Insuch an example, the host unit 105 can send and receive modulated analogRF signals with the host unit 105. The host unit 105 can convert betweenthe modulated RF signals and modulated analog IF signals, which aretransported between the host unit 105 and AAUs 110-1 to 110-n.

In some examples, DAS 103 can be an analog and digital DAS and transportboth signals including digital samples and analog modulated IF signalsconcurrently.

The AAUs 110-1 to 110-n perform similar conversions for digital andanalog DAS functions respectively. In the uplink of a digital DASexample, a AAU 110-1 to 110-n senses a modulated wireless RF signal viaan antenna, down converts the RF signal to IF, digitizes (A/D converts)the IF signal to produce real digital IF samples, digitallydown-converts the real digital IF samples to produce I/Q (complex)samples, and incorporates the I/Q samples into a downlink transportsignal. In some embodiments, the I/Q samples are resampled. In someembodiments, any of the analog signals or digital samples can befiltered to select only a portion of the original bandwidth fortransport. In the downlink of this digital DAS example, the AAU 110-1 to110-n receives an uplink transport signal from the host unit 105,extracts the I/Q samples therefrom, digitally up-converts the I/Qsamples to produce real digital IF samples, D/A converts the realdigital IF samples to a modulated analog IF signal, up-converts theanalog IF signal to an RF signal, amplifies and radiates a wireless RFsignal to one or more wireless units 128.

The DAS 100 also includes a location estimation module 102 to estimate alocation of a wireless unit 128 that is communicating through the DAS100. In the example shown in FIG. 1, the location estimation module 102is implemented by the host unit 105. In other examples, however, thelocation estimation module 102 can be a standalone unit or can beimplemented by one of the AAUs 110. The location estimation module 102can be implemented as instructions stored on a processor readable mediumand configured to cause one or more processors, when executed thereby,to implement the functionality described herein.

FIG. 2 is a flow diagram of an example method 200 for estimating alocation of a wireless unit with a DAS 100. In an example, the locationestimation process is initiated by a request from a baseband unit or aserving mobile location center (SMLC) to the location estimation module102 to estimate a location of a wireless unit 128 that has beenallocated to a first time and frequency unit in the uplink RF spectrum(block 202). The baseband unit or SMLC can be located in a deviceupstream from the host unit 105, such as a base station 115, or can belocated in the host unit 105 itself. In an example, the basebandunit/SMLC initiates a request to estimate a location based on anemergency call being received from the wireless unit 128. In particular,the baseband unit/SMLC upon receiving the emergency uplink signal fromthe wireless unit 128 implements the location estimation process for thewireless device 128. To implement the location estimation process, thebaseband unit/SMLC sends a request to the location estimation module102, wherein the request indicates a time and frequency unit allocatedto the wireless unit 128 in which the location estimation is to bedetermined. The baseband unit/SMLC being able to modulate and demodulatethe wireless RF signals, knows the identity and resource allocations forthe wireless unit 128. The DAS 100, however, does not typicallydemodulate the signals generated by the baseband unit or the wirelessunit 128. Thus, the DAS 100 does not know the identity of the wirelessdevice 128 or the resources that are allocated to the wireless device128. Accordingly, the baseband unit/SMLC identifies the resources (e.g.,the time and frequency unit(s)) that are allocated to the wireless unit128 in which the location is to be estimated, and sends the time andfrequency unit(s) in the request to the location estimation module 102.

The time and frequency unit(s) are time and frequency unit(s) of the RFcommunication protocol used for communication between the baseband unitand the wireless units 128. In an example, the baseband unit and thewireless units 128 communicate using a protocol that conforms to along-term evolution (LTE) standard. In such an example, a time andfrequency unit is a resource element as defined by the LTE standard.Typically, multiple resource elements (referred to as a resource block)are allocated to a given wireless unit 128. Accordingly, in an example,the time and frequency unit(s) in the request sent from the basebandunit are resource element(s) of an LTE protocol. In a particularexample, the time and frequency unit(s) are a resource block of an LTEprotocol. In other examples, the baseband unit and the wireless units128 communicate using other protocols including but not limited to otherOFDM systems (e.g., WiMAX) and TDMA-FDMA systems (e.g., GSM, IS-136TDMA), and the time and frequency unit(s) are allocated elements of therespective protocol.

In examples where the host unit 105 communicates with the upstreamdevice (e.g., base station 115) using baseband data (e.g., CPRIsignals), the upstream device provides the host unit 105 with a map ofthe time and frequency units available in the RF signals between thebaseband unit and the wireless unit(s) 128. By virtue of this map, thelocation estimation module 102 knows the time and frequency units thatcan be allocated to a given wireless unit 128. In examples where thehost unit 105 communicates with the upstream device (e.g., base station115) using RF signals, the host unit 105 can be configured to demodulatea downstream control channel from the upstream device to obtain the mapof time and frequency units available in the RF signals between thebaseband unit and the wireless unit(s) 128. In other examples, the hostunit 105 can be configured to receive the map of time and frequencyunits from the upstream device over an auxiliary channel. In any case,the host unit 105 can provide the map of time and frequency units to thelocation estimation module 102 and/or AAUs 110 if appropriate.

Upon receiving the request from the baseband unit/SMLC, the locationestimation module 102 send out a command to the AAUs 110 to identify atime of arrival of an uplink wireless RF signal in the time andfrequency unit(s) indicated in the request from the baseband unit/SMLC(block 204). The command from the location estimation module 102 can besent in any suitable manner, such as by using a communication channelimplemented in the DAS 100 between the host unit 102 and the AAUs 110.

Upon receiving the command from the location estimation module 102, eachAAUs 110 identifies a time of arrival of an uplink wireless signal inthe time and frequency unit(s) indicated in the command from thelocation estimation module 102 (block 206). Each AAUs individuallydetermines its own time of arrival of the wireless RF signal. An AAU candetermine this time of arrival by listening for a signal in the time andfrequency unit(s) indicated and can time stamp such a signal if it ispresent. Since the time of arrival of a signal at an AAU 110 is based ona physical distance that the wireless unit 128 is from the AAU 110, thetime of arrival of a wireless signal from the wireless unit 128 at eachAAU 110 can be different. If an AAU 110 is not in range of the wirelesssignal from the wireless unit 128, that AAU 110 will not sense awireless signal and, accordingly, will not identify a time of arrival.If an AAU 110 is within range of the wireless signal form the wirelessunit 128, the AAU 110 can sense the wireless signal and determine thetime of arrival of the signal. Ideally, multiple AAUs 110 will be ableto sense the wireless signal and determine the time of arrival thereof.Notably, the AAUs 110 are identifying the time of arrival of a signal inthe time and frequency unit(s) indicated in the command from thelocation estimation module 102. That is, if a wireless signal is sensedin a time and frequency unit that is not included in the time andfrequency unit(s) indicated by the location estimation module 102, thetime of arrival of such a signal is not relevant for the locationestimation as such a signal is not from the wireless unit 128 in whichthe location is to be determined.

In an example, the wireless signal from the wireless unit 128 in thetime and frequency unit(s) that is time stamped by the AAUs 110 is anon-location purpose signal that is transmitted to communicateinformation (e.g., voice signals or data) to another device (e.g., toanother telephone or computer). For example, the wireless signal can bea wireless transmission in the ordinary course of communicating by thewireless unit 128. Accordingly, the time and frequency unit(s) allocatedto the wireless unit 128 can be general purpose time and frequencyunit(s) that could be allocated to any similar wireless unit 128. Inanother example, the wireless signal from the wireless unit 128 is acontrol signal that occurs in known time and frequency unit(s), such asan uplink sounding signal or a demodulation reference signal.

In another example, the wireless signal from the wireless unit 128 inthe time and frequency unit(s) that is time stamped is a special purposesignal that the wireless unit 128 transmits specifically for determiningits location. In an implementation of such an example, the wirelesssignal may have increased power or may be transmitted in special purposetime and frequency unit(s) such as time and frequency unit(s) allocatedfor determining a location of a wireless unit 128. In an implementationof such an example, a command need not be sent from a baseband unit/SMLCto a location estimation module 102 to initiate the location estimationprocess. Instead, the AAUs 110 can continuously monitor the time andfrequency unit(s) allocated for location determination and if a wirelesssignal is received in the time and frequency unit(s), identify a time ofarrival of the wireless signal. In such an example, the wireless unit128 can be configured to automatically transmit a signal in the specialpurpose time and frequency unit(s) allocated to determine location incertain circumstances (e.g., if a 911 call is initiated), or thewireless unit 128 can be commanded to transmit a signal in the specialpurpose time and frequency unit(s) by the baseband unit.

If an AAU 110 senses a wireless signal in the time and frequencyunit(s), the AAU 110 can determine the time of arrival of the signal atthe AAU 110. The AAU 110 can determine this time of arrival in anysuitable manner such as by signal envelope detection, correlation withreferences, or cross correlation between signals. The AAU 110 then sendsthe time of arrival of the signal to the location estimation module 102(block 208). Accordingly, the location estimation module 102 can receivea first time of arrival from a first AAU 110-1, wherein the first timeof arrival is a time of arrival of the wireless signal from the wirelessunit 128 at the first AAU 110-1. The location estimation module 102 canalso receive a second time of arrival from a second AAU 110-2, whereinthe second time of arrival is a time of arrival of the wireless signalfrom the wireless unit 128 at the second AAU 110-2. The locationestimation module 102 can also receive a third time of arrival from athird AAU 110-2, wherein the third time of arrival is a time of arrivalof the wireless signal from the wireless unit 128 at the third AAU110-3.

In an example, only AAUs 110 that sense a wireless signal in the timeand frequency unit(s) send a message to the location estimation module102, wherein the message includes the corresponding time of arrival. Inanother example, all AAUs 110 send a message to the location estimationmodule 102, whereby AAUs 110 that do not sense a wireless signal in thetime and frequency unit(s) send a message indicating that they did notsense a wireless signal in the time and frequency unit(s).

Upon receiving the times of arrival from a plurality of the AAUs 110,the location estimation module 102 can estimate a location of thewireless unit 128 based on a difference between the multiple times ofarrival (block 210). The location estimation module 102 can have adatabase accessible thereby that includes the physical location of eachof the AAUs 110. Using this information and the times of arrival of thewireless signal at multiple AAUs 110, the location estimation module 102can estimate a location of the wireless unit 128. In an example, thelocation estimation module 102 can use multi-lateration to estimate thelocation of the wireless unit 128 corresponding to the wireless signalin the time and frequency unit(s) indicated.

In an example, the AAUs 110 can also send to the location estimationmodule 102, an indication of the time and frequency unit(s)corresponding to their respective time of arrival. Such an indication ofthe time and frequency unit(s) can be beneficial if multiple locationestimation procedures are being implemented concurrently. If so, sendingan indication of the time and frequency unit(s) corresponding to thetime of arrival information identifies which location estimationprocedure the time of arrival information pertains to. Such anindication of the time and frequency unit(s) corresponding to the timeof arrival can be made in any suitable manner such as by a reference tothe command from the location estimation module to obtain the time ofarrival or by sending a resource element or resource block with the timeof arrival information.

Upon estimating a location, the location estimation module 102 can sendthe location to the baseband unit/SMLC (block 212). In examples wherethe baseband unit/SMLC is in an upstream device (e.g., base station115), the location estimation module 102 can send the location to thebase station 115. The location determined by the location estimationmodule 102 can be any appropriate location, such as a globallyreferenced location (e.g., latitude and longitude coordinates), a rangeof locations, a locally referenced location (e.g., floor 5 of thebuilding 315, section 21 of a stadium, near the corner of 10^(th) andMarquette in Minneapolis), a location with reference to the location ofthe host unit 105 or the location of the base station (e.g., 300 feetsouth of host unit 105), or other location. The location can be providedin any suitable format. For example, the location can be provided to thebaseband unit/SMLC in coordinates of the global coordinate system (e.g.,latitude and longitude). In another example, the location can beprovided in terms relative to the location of the AAUs 110 (e.g., 1^(st)floor, NE corner of XXX building, or Office 301). In some examples,multiple of such location formats can be provided to the basebandunit/SMLC.

In some examples, the location estimation module 102 can send to thebaseband unit/SMLC, an indication of the time and frequency unit(s)corresponding to the location. Such an indication of the time andfrequency unit(s) can be beneficial if multiple location estimationprocedures are being implemented concurrently. If so, sending anindication of the time and frequency unit(s) corresponding to thelocation information identifies which location estimation procedure thelocation pertains to. Such an indication of the time and frequencyunit(s) corresponding to the location can be made in any suitable mannersuch as by a reference to the request from the baseband unit/SMLC toobtain the location or by sending a resource element or resource blockwith the location information.

In some examples, the location estimation module 102 can calculate otherdata for the wireless unit 128 communicating over respective time andfrequency unit(s). Such other data can include a power levelcorresponding to the signal(s) received from the wireless unit 128, aspeed, direction, or velocity (both speed and direction) of motion ofthe wireless unit 128, and/or an angle from which a wireless signal fromthe wireless unit 128 is received at a given AAU 110. This other datacan be provided to the baseband unit/SMLC along with the indication ofthe time and frequency unit(s) corresponding thereto as discussed above.In some examples, this other data can also be used to determine alocation for the wireless unit 128.

In exemplary embodiments, cellular RF signals may utilize variouswireless protocols and in various bands of frequency spectrum. Forexample, the cellular RF signals may include, but are not limited to,licensed RF bands, 800 MHz cellular service, 1.9 GHz PersonalCommunication Services (PCS), Specialized Mobile Radio (SMR) services,Enhanced Special Mobile Radio (ESMR) services at both 800 MHz and 900MHz, 1800 MHz and 2100 MHz Advanced Wireless Services (AWS), 700 MHzuC/ABC services, two way paging services, video services, Public Safety(PS) services at 450 MHz, 900 MHz and 1800 MHz Global System for MobileCommunications (GSM), 2100 MHz Universal Mobile TelecommunicationsSystem (UMTS), Worldwide Interoperability for Microwave Access (WiMAX),3rd Generation Partnership Projects (3GPP) Long Term Evolution (LTE),High Speed Packet Access (HSPA), or other appropriate communicationservices. The system described herein are capable of transporting bothSingle Input Single Output (SISO) and Multiple Input Multiple Output(MIMO) services at any of the frequencies described above. The systemsdescribed herein can support any combination of SISO and MIMO signalsacross various bands of frequency spectrum. In some example embodiments,the systems described herein may provide MIMO streams for WiMAX, LTE,and HSPA services while only providing SISO streams for other services.Other combinations of MIMO and SISO services are used in otherembodiments.

In examples, any of the processors described above may include orfunction with software programs, firmware or other computer readableinstructions for carrying out various methods, process tasks,calculations, and control functions, used in the digital processingfunctionality described herein. These instructions are typically storedon any appropriate computer readable medium used for storage of computerreadable instructions or data structures. The computer readable mediumcan be implemented as any available media that can be accessed by ageneral purpose processor (GPP) or special purpose computer or processor(such as a field-programmable gate array (FPGA), application-specificintegrated circuit (ASIC) or other integrated circuit), or anyprogrammable logic device. Suitable processor-readable media may includestorage or memory media such as magnetic or optical media. For example,storage or memory media may include conventional hard disks, CompactDisk-Read Only Memory (CD-ROM), volatile or non-volatile media such asRandom Access Memory (RAM) (including, but not limited to, SynchronousDynamic Random Access Memory (SDRAM), Double Data Rate (DDR) RAM, RAMBUSDynamic RAM (RDRAM), Static RAM (SRAM), etc.), Read Only Memory (ROM),Electrically Erasable Programmable ROM (EEPROM), and flash memory, etc.Suitable processor-readable media may also include transmission mediasuch as electrical, electromagnetic, or digital signals, conveyed via acommunication medium such as a network and/or a wireless like.

Example Embodiments

Example 1 includes a method for obtaining location information regardinga wireless unit in a distributed antenna system (DAS), the methodcomprising: identifying a first time of arrival of a wireless signal ina time and frequency unit at a first active antenna unit (AAU);identifying a second time of arrival of the wireless signal in the timeand frequency unit at a second AAU; estimating a location of a wirelessunit transmitting the wireless signal based on a location of the firstAAU, a location of the second AAU, and a difference between the firsttime of arrival and the second time of arrival; and sending to abaseband unit or serving mobile location center (SMLC), the location ofthe wireless unit and an indication that the location corresponds to thetime and frequency unit.

Example 2 includes the method of Example 1, comprising: identifying athird time of arrival of the wireless signal in the time and frequencyunit at a third AAU, wherein estimating a location includes estimating alocation based on a location of the third AAU and a difference betweenthe third time of arrival, the first time of arrival, and the secondtime of arrival.

Example 3 includes the method of any of Examples 1-2, wherein the timeand frequency unit is a resource element of a communication protocolconforming to a long-term evolution (LTE) standard.

Example 4 includes the method of Example 3, wherein the indication thatthe location corresponds to the time and frequency unit includes anindication that the location corresponds to a resource block thatincludes the resource element.

Example 5 includes the method of any of Examples 1-4, comprising:receiving a map of an allocation of time and frequency units from abaseband unit; and determining the time and frequency unit of the firstsignal and the second signal based on the map.

Example 6 includes the method of any of Examples 1-5, wherein estimatinga location includes using multi-lateration to determine the location.

Example 7 includes the method of any of Examples 1-6, comprising:demodulating a downlink control channel to determine a map of anallocation of time and frequency units in the uplink; and determiningthe time and frequency unit of the first signal and the second signalbased on the map.

Example 8 includes the method of any of Examples 1-7, comprising:sending the first time of arrival from the first AAU to a locationestimation module; and sending the second time of arrival from thesecond AAU to a location estimation module, wherein estimating thelocation includes estimating the location with the location estimationmodule and wherein sending the location to the baseband unit or SMLCincludes sending the location from the location estimation module to thebaseband unit or SMLC.

Example 9 includes the method of any of Examples 1-8, comprising:sending an indication that the first time of arrival corresponds to thetime and frequency unit from the first AAU to the location estimationmodule; and sending an indication that the second time of arrivalcorresponds to the time and frequency unit from the second AAU to thelocation estimation module.

Example 10 includes the method of any of Examples 1-9, comprising:receiving a request from the baseband unit or SMLC to determine alocation of a wireless unit that is allocated the time and frequencyunit of the wireless signal in the uplink.

Example 11 includes a distributed antenna system (DAS) comprising: ahost unit; a plurality of active antenna units (AAUs) communicativelycoupled to the host unit over a respective communication link 125, theAAUs configured to wirelessly communicate with one or more wirelessdevices, wherein a first AAU of the plurality of AAUs is configured toidentify a first time of arrival of a wireless signal in a time andfrequency unit, wherein a second AAU of the plurality of AAUs isconfigured to identify a second time of arrival of the wireless signalin a time and frequency unit; wherein a location estimation module isconfigured to estimate a location of a wireless unit transmitting thewireless signal based on a location of the first AAU, a location of thesecond AAU, and a different between the first time of arrival and thesecond time of arrival, wherein the location estimation module isconfigured to send to the baseband unit or a serving mobile locationcenter (SMLC), the location of the wireless unit and an indication thatthe location corresponds to the time and frequency unit.

Example 12 includes the DAS of Example 11, wherein a third AAU of theplurality of AAUs is configured to identify a third time of arrival ofthe wireless signal in a time and frequency unit, wherein the locationestimation module is configured to estimate a location of a wirelessunit transmitting the wireless signal based on a location of the thirdAAU and a difference between the third time of arrival, the first timeof arrival, and the second time of arrival.

Example 13 includes the DAS of any of Examples 11-12, wherein the timeand frequency unit is a resource element of a communication protocolconforming to a long-term evolution (LTE) standard.

Example 14 includes the DAS of Example 13, wherein the indication thatthe location corresponds to the time and frequency unit includes anindication that the location corresponds to a resource block thatincludes the resource element.

Example 15 includes the DAS of any of Examples 11-14, wherein thelocation estimation module is configured to use multi-lateration todetermine the location.

Example 16 includes the DAS of any of Examples 11-15, wherein thelocation estimation module is implemented by the host unit.

Example 17 includes a method of estimating a location of a wireless unitwith a distributed antenna system (DAS), the method comprising:receiving a request at a location estimation module in the DAS from aserving mobile location center (SMLC) to determine a location of awireless unit allocated to a first time and frequency unit in the uplinkRF spectrum; sending a command from the location estimation module to aplurality of AAUs of the DAS to generate determine respective times ofarrival for a wireless signal in the first time and frequency unit;identifying a first time of arrival of a wireless signal in the firsttime and frequency unit; identifying a second time of arrival of thewireless signal in the first time and frequency unit; sending the firsttime of arrival from the first AAU to the location estimation module;sending the second time of arrival from the second AAU to the locationestimation module; estimating a location of the wireless unit based on alocation of the first AAU, a location of the second AAU, and adifference between the first time of arrival and a second time ofarrival; and sending the location of the wireless unit to the SMLC.

Example 18 includes the method of Example 17, comprising: identifying athird time of arrival of the wireless signal in the first time andfrequency unit at a third AAU; wherein estimating a location includesestimating a location based on the location of the third AAU and adifference between the third time of arrival, the first time of arrival,and the second time of arrival.

Example 19 includes the method of any of Examples 17-18, wherein thefirst time and frequency unit is a resource element of a communicationprotocol conforming to a long-term evolution (LTE) standard.

Example 20 includes the method of Example 19, wherein the requestidentifies a resource block in the uplink RF spectrum that is allocatedto the wireless unit.

What is claimed is:
 1. A method for obtaining location informationregarding a wireless unit in a distributed antenna system (DAS), themethod comprising: identifying a first time of arrival of a wirelesssignal in a time and frequency unit at a first active antenna unit(AAU); identifying a second time of arrival of the wireless signal inthe time and frequency unit at a second AAU; receiving a map of anallocation of time and frequency units; determining the time andfrequency unit of the signal based on the map; and estimating a locationof a wireless unit transmitting the wireless signal based on a locationof the first AAU, a location of the second AAU, and a difference betweenthe first time of arrival and the second time of arrival.
 2. The methodof claim 1, comprising: identifying a third time of arrival of thewireless signal in the time and frequency unit at a third AAU, whereinestimating a location includes estimating a location based on a locationof the third AAU and a difference between the third time of arrival, thefirst time of arrival, and the second time of arrival.
 3. The method ofclaim 1, wherein the time and frequency unit is a resource element of acommunication protocol conforming to a long-term evolution (LTE)standard.
 4. The method of claim 3, wherein the indication that thelocation corresponds to the time and frequency unit includes anindication that the location corresponds to a resource block thatincludes the resource element.
 5. The method of claim 1, whereinestimating a location includes using multi-lateration to determine thelocation.
 6. The method of claim 1, comprising: demodulating a downlinkcontrol channel to determine the map of the allocation of the time andfrequency units in the uplink; and determining the time and frequencyunit of the signal based on the map.
 7. The method of claim 1,comprising: sending an indication that the first time of arrivalcorresponds to the time and frequency unit from the first AAU to alocation estimation module; and sending an indication that the secondtime of arrival corresponds to the time and frequency unit from thesecond AAU to the location estimation module.
 8. The method of claim 1,comprising: receiving a request to determine a location of a wirelessunit that is allocated the time and frequency unit of the wirelesssignal in the uplink.
 9. The method of claim 1, comprising: sending thefirst time of arrival from the first AAU to a location estimationmodule; and sending the second time of arrival from the second AAU tothe location estimation module, wherein estimating the location includesestimating the location with the location estimation module.
 10. Adistributed antenna system (DAS) comprising: a host unit; a plurality ofactive antenna units (AAUs) communicatively coupled to the host unitover a respective communication link, the AAUs configured to wirelesslycommunicate with one or more wireless devices, wherein a first AAU ofthe plurality of AAUs is configured to identify a first time of arrivalof a wireless signal in a time and frequency unit and to send the firsttime of arrival to a location estimation module comprising processingcircuitry; wherein a second AAU of the plurality of AAUs is configuredto identify a second time of arrival of the wireless signal in a timeand frequency unit and to send the second time of arrival from thesecond AAU to the location estimation module; wherein the locationestimation module is configured to estimate a location of a wirelessunit transmitting the wireless signal based on a location of the firstAAU, a location of the second AAU, and a difference between the firsttime of arrival and the second time of arrival; and wherein the hostunit is configured to receive a map of an allocation of time andfrequency units, and to determine the time and frequency unit of thefirst signal and the second signal based on the map.
 11. The DAS ofclaim 10, wherein a third AAU of the plurality of AAUs is configured toidentify a third time of arrival of the wireless signal in a time andfrequency unit, wherein the location estimation module is configured toestimate a location of a wireless unit transmitting the wireless signalbased on a location of the third AAU and a difference between the thirdtime of arrival, the first time of arrival, and the second time ofarrival.
 12. The DAS of claim 10, wherein the time and frequency unit isa resource element of a communication protocol conforming to a long-termevolution (LTE) standard.
 13. The DAS of claim 12, wherein theindication that the location corresponds to the time and frequency unitincludes an indication that the location corresponds to a resource blockthat includes the resource element.
 14. The DAS of claim 10, wherein thelocation estimation module is configured to use multi-lateration todetermine the location.
 15. The DAS of claim 10, wherein the locationestimation module is implemented by the host unit.
 16. A method ofestimating a location of a wireless unit with a distributed antennasystem (DAS), the method comprising: receiving a request at a locationestimation module in the DAS to determine a location of a wireless unitallocated to a first time and frequency unit in the uplink RF spectrum;wherein the request identifies a resource block in the uplink RFspectrum that is allocated to the wireless unit; sending a command fromthe location estimation module to a plurality of AAUs of the DAS todetermine respective times of arrival for a wireless signal in the firsttime and frequency unit; identifying a first time of arrival of awireless signal in the first time and frequency unit; identifying asecond time of arrival of the wireless signal in the first time andfrequency unit; sending the first time of arrival from the first AAU tothe location estimation module; sending the second time of arrival fromthe second AAU to the location estimation module; and estimating alocation of the wireless unit based on a location of the first AAU, alocation of the second AAU, and a difference between the first time ofarrival and a second time of arrival.
 17. The method of claim 16,comprising: identifying a third time of arrival of the wireless signalin the first time and frequency unit at a third AAU, wherein estimatinga location includes estimating a location based on the location of thethird AAU and a difference between the third time of arrival, the firsttime of arrival, and the second time of arrival.
 18. The method of claim16, wherein the first time and frequency unit is a resource element of acommunication protocol conforming to a long-term evolution (LTE)standard.